The flapper-type toilet tank valve is one of the best known and most widely used valves in the world. It is installed in a tank where it holds back a volume of water sufficient when released to flush a commode or a urinal. The water is admitted to the tank by another valve, often called a tank valve or a ballcock valve, which refills the tank after the flush valve is closed, to complete a flushing cycle.
The flush valve is usually installed in an outlet port in the bottom of the tank, along with a standpipe that discharges into the outlet port downstream from the tank valve itself.
The tank valve includes a valve seat which surrounds an outlet passage that discharges to the outlet port. A flapper is pivotally mounted to fixed structure, usually the standpipe, and carries a valve seal that bears against the valve seat to close the valve in a lowered position, and which is movable up and away from the seat to open the valve. A lift chain is usually provided to lift the flapper and open the valve. The chain is connected through a linkage to a handle actuated by the user.
A frequently-encountered mounting means for attachment for the flapper is a pair of diametrically extending posts on the standpipe, and each of these posts has an upwardly extending ear spaced from the standpipe. This arrangement is particularly useful when the entire flapper is made of rubber, and is in a single piece. Then apertured arms of the resilient flapper are twisted to get them over the ears and relaxed to surround the posts which act as a pivot for the arms. This is a device which has sold by the millions for many years, and in many applications is completely reliable for long periods of time. It is readily molded and very affordable.
However, in recent years the water in some tanks to which the rubber flappers are subjected has attacked the rubber of which an affordable single piece cast flapper valve can be made. There are some rubber compounds that can resist this attack, but they are relatively costly. Affordable organic plastic materials that can resist this attack are rigid, and if provided as a single piece valve cannot be attached to the conventional mounting means because they cannot be twisted, and also because the ears prevent the arms from being sprung over the posts. Thus, when a resilient rubber flapper valve that is fitted to the described posts fails, the flapper must either be replaced with another that is likely to suffer a similar fate, or the entire assembly of threaded base, valve seat, standpipe, and some other kind of mounting means must be replaced. An inexpensive, more chemically-resistant flapper cannot merely be substituted for the failed resilient flapper.
It is an object of this invention to provide a flapper with a rigid construction that can be made of suitably chemically-resistant material and which can be installed on a conventional post-and-ear mounting at an agreeable and competitive cost.
However, affordable rigid materials cannot themselves make a suitable fluid seal with the customary rigid seats on flush valves. Accordingly, a suitably deformable and resilient material must be provided for this purpose. Such materials must resist chemical attack and are relatively costly. They should be minimized. Molded shapes adhered to rigid structure, while useful, involve still more cost and complexity.
An optimal seal would be a simple flexible disc adapted both by its flexural and deformable properties to making a good fluid seal. It could affordably be made of a minimal quantity of costlier chemically resistant material. However, a surprising result sometimes occurs. When such a disc, bound to and surrounding a central post a backed up by a flat backing disc, seals on a hard seat, after a brief period of time the valve begins to leak. This is a perplexing event because one can readily theorize that the disc should merely flex and deform to fit to the valve seat.
Efforts to overcome this surprising leakage while still using a flat disk for a seal have shown that unbalanced forces seem to develop unless the region between the backing plate and the valve seal is equalized with the tank pressure. The reasons are not fully understood, but the result is that a optimum valve can be made, and the perplexing leakage does not occur.